1. Field of the Invention
The present invention relates to an optical disk player and, more particularly, to an optical disk player which records and/or reproduces data on an optical disk.
2. Description of the Prior Art
Optical disk players in which a laser beam is radiated onto an optical disk to write information on the disk or read information from it are widely used. Optical disks are effectively used as a medium to store voice and video signals and other forms of data, finding their applications in such apparatus as compact disk, television game, and video disk players.
All of these optical disk players require a track-following servo system for correctly forming a beam spot on a recording track on a rotating optical disk to read or write information on it. Usually, this track-following servo system has both a roughly operating actuator (thread mechanism) driven by a linear motor or other means to move an entire optical head in the radial direction of an optical disk and a biaxial mechanism to move the objective in the optical head in the tracking direction (parallel to the surface of the optical disk and across recording tracks) and focus direction (vertical to the surface of the optical disk and parallel to the optical axis of the objective). These tracking control mechanisms are controlled by a tracking error signal obtained by processing the output signal from the optical head.
Illustratively, when starting a recorded-information reproducing operation on a player which reads an optical disk such as a compact disk, a focus servo operation is activated to be closed and a rough spindle servo operation for a spindle motor to rotate the compact disk is performed, followed by a track positioning operation controlled by the biaxial mechanism to position the optical head to the specified recording track. When the track positioning operation has been completed, the biaxial mechanism and the thread mechanism are controlled so that the laser beam correctly follow the recording track while, on the compact disk player, the rough spindle servo operation is activated to close the servo loop.
It should be noted that optical disks on which data are recorded and/or reproduced by the optical disk player are slightly uneven from disk to disk in the reflectivity of the recording or reflective medium coated on disk or may have scratches on the recording medium. However, since the tracking error signal is generated from the output of a detector which senses the laser beam reflected from the optical disk, an unstable tracking servo operation may result unless the status of the reflected beam is stable. The unstable tracking servo operation especially causes a lengthy tracking servo positioning operation.
It should also be noted that when an optical disk is chucked, it is unavoidably held slightly off-center. This eccentricity also makes it difficult to perform a correct tracking operation, necessarily causing problems such as a lengthy tracking servo positioning operation and the generation of servo noises.